JEE PYQ: Binomial Theorem Question 29
Question 29 - 2020 (07 Jan Shift 1)
The greatest positive integer $k$, for which $49^k + 1$ is a factor of the sum $49^{125} + 49^{124} + \ldots + 49^2 + 49 + 1$, is:
(1) 32 (2) 63 (3) 60 (4) 65
Show Answer
Answer: (2)
Solution
Sum $= \frac{49^{126}-1}{48}$. $49^k + 1$ divides $49^{63}+1$ when $k | 63$. Largest $k = 63$.